1. Field of the Invention
Aspects of the present invention relate to a secondary battery, and more particularly, to an electrode assembly and a lithium secondary battery using the same.
2. Description of the Related Art
Generally, a secondary battery is a battery that can be repeatedly charged and discharged, differently from a disposable battery that is not rechargeable. Secondary batteries have been widely used for advanced electronic devices such as cellular phones, notebook computers and camcorders.
In particular, lithium secondary batteries are developing rapidly because they have an operating voltage of 3.6 V that is three times more than a nickel-cadmium battery or a nickel-hydrogen battery, and they have high energy density per unit weight. Lithium secondary batteries use lithium group oxides as a cathode active material, and carbon materials as an anode active material. Depending on the kind of electrolyte, lithium secondary batteries are divided into liquid electrolyte batteries and polymer electrolyte batteries. Batteries using liquid electrolyte are called lithium ion batteries and batteries using a polymer electrolyte are called lithium polymer batteries. In addition, lithium secondary batteries are classified according to the shape of their cases into cylindrical, angular and pouch types.
An electrode assembly is provided inside the case of a lithium secondary battery. The electrode assembly is formed by interposing a separator between cathode and anode plates and winding all three together. The cathode and anode plates are formed of a collector and an active material layer coated on at least one surface of the collector. Both ends of the collector include uncoated portions where the active material layer is not formed. Usually, electrode tabs are provided at the uncoated portions.
Usually, at the portions of the battery where the electrode tabs are welded to the electrode plates, metals of different composition are electrically coupled to each other, that is, the metals of the electrode plates and the metals of the electrode tabs. Accordingly, the internal resistance (IR) of those portions increases and significant heat is generated. Therefore, protective tapes are attached to protect the portions where the electrode plates and electrode tabs are electrically coupled to each other.
In addition, insulation tape is attached to the boundaries between the electrode tab installation portions, the active material layers and the uncoated portions. The insulation tape attached to the boundaries between the active material layers and uncoated portions prevents short circuits that could be caused by contact between the electrode plates or the tab for one electrode plate and the other electrode plate.
However, the protective tape or insulation tape is attached only to a partial region of an electrode plate. Meanwhile, the separator insulating the electrode plates from each other contracts from the internal heat generated by a nearby electrode tab. Thus, the uncoated portion of the one electrode plate without the insulation tape and the active material layer of the other electrode plate become electrically coupled to each other, thereby causing an internal short circuit of the battery. In addition, the internal short circuit of the battery may occur by contact between the uncoated portions of the two electrode plates. The internal short circuit may cause accidents such as fire or explosion of the battery thus adversely affecting the reliability of the battery.